<template>
    <div class="child">
     <h3>我是child组件(子) </h3>
     {{sum}}
    </div>
   </template>
   
   <script>
    import {ref} from 'vue'
     export default{
       name:'child',
       async setup(){
        let sum = ref(0);
        let p = new Promise((resolve,reject)=>{
          setTimeout(()=>{
            resolve({sum})
          },3000)
        })
        return await p
       }

     }
   </script>
   
   <style>
     .child{
       background-color: skyblue;
       padding: 10px;
     }
   </style>
   